State of dispersion of impurity on formation of Z1-centres in NaCl:Sr2+ crystals

Thermoluminescence (TL) and Optical absorption studies are carried out to study the bleaching kinetics of F-centre and formation of Z₁-centres in X-irradiated strontium doped NaCl crystals, both in as-grown state and in quenched state. An additional TL peak is observed in this crystal system after F-bleaching of irradiated samples which is attributed to thermal annealing of Z₁-centres. Various models proposed for Z₁-centres are reviewed in the light of these results and it is concluded that Z₁-centres are associated with impurity-vacancy dipoles.     

Role of Z1 centres in radiation hardening of NaCl:Ba2+ crystals

Radiation hardening studies of undoped NaCl and NaCl crystals doped with barium have been carried out both in the as-grown state and after quenching them from 650°C. It is observed that the radiation hardening is more in doped crystals and the results are explained taking into consideration the role of Z₁-centres.     

Contribution of Z1-centers in radiation hardening of NaCl: Sm2+ crystals — a study

Microhardness studies on X-irradiated NaCl and NaCl:Sm crystals are studied with varying times of X-irradiation in pre-quenched and quenched crystals. The contribution of Z₁-centers in radiation hardening studies is discussed.     

A study of complex glow curves of Quenched NaCl:Ca crystals

Glow curves of the thermally pretreated NaCl:Ca crystals are recorded and are found to be complex in nature. The complex glow curve is analysed using thermal cleaning technique and the trap parameters are calculated by various methods. The glow peaks have been tentatively attributed to impurity and various types of colour centers.     

A Study of precipitation morphology in NaCl:Sr and NaCl:Ba crystals

Single crystals of sodium chloride grown from melt containing different concentrations of strontium and barium have been observed to contain a second phase precipitating throughout the interior in the form of thin rods and well defined polygonal platelets. Two types of rods have been observed, one type oriented along 〈100〉 and the other along 〈110〉 directions. The platelets are variously in the form of hexagons, octagons, and rhombs. The precipitates disappear on quenching the crystal and reappear on aging the crystals under suitable conditions.     

A study of Z1-centers in γ-irradiated KCl:Ba2+ crystals

The purpose of the paper is to report the optical absorption and thermoluminescence measurements on KCl: Ba²⁺ crystal irradiated with γ-rays. Bleaching in F-band increases the glow peak around 75 °C and suppresses the 125 °C peak. A similar result is observed in preheat treated crystals. When this peak is thermally cleaned, the broadening of the absorption on the prolonged F-bleached crystals is removed. On the basis of these observations, the glow peak at 75 °C is tentatively attributed to Z₁-centers.     

Effect of Flux on thermoluminescence in Flux-grown BaFCl crystals

BaFCl crystals have been grown using BaF₂ and BaCl₂ by flux technique. Glow curves, optical absorption, and TL emission spectra of x/r — irradiated crystals are studied. The results have been compared with those BaFCl crystals grown from NaF flux so as to study the effects of flux on these properties. It is found that crystals grown from BaF₂ flux are relatively purer. An additional TL glow peak at 460 K, an optical absorption band at 775 nm and TL emission band at 485 nm have been obtained in the presently grown crystals. The additional glow peak, optical absorption band have been attributed to F(¯F) aggregate centers, whereas the 485 nm TL emission band to impurity centers.     

Evaporation of doped NaCl crystals

In the present paper an investigation of the influence of impurity ions on the evaporation of NaCl crystals is reported. Monovalent impurities little influence the evaporation rate. The evaporating structures have changed only when there were extremal differences in the values of ionic radii. However, the bivalent impurities substantially influence the evaporation rate. This unfluence depends upon the fact whether the impurities are in non-associated or associated state with cation vacancies, respectively. This fact also affects the shape of evaporating structure.     

Morphology and orientation relations of BaCl2 precipitates in NaCl single crystals

In the present paper morphology and orientation relations of BaCl₂ precipitates in NaCl single crystals are described. It is shown that BaCl₂ precipitates of large dimensions are formed at the dislocations of a/2〈110〉{100}, the dislocation lines of which are oriented in the directions 〈210〉.     

Etch-pit study of dislocation microstructure at the precipitates in NaCl:Ni crystals

The chemical etching technique was used to study the precipitation-induced dislocation microstructures in NaCl:Ni crystals with 110 rod-like precipitates. The comparison was made of the results obtained by the etch pit and decoration studies. The coincidence of the patterns suggests the prismatic dislocation loops and helices of the interstitial type to be only produced at elevated temperatures (above 300°C). The smallest size loops are removed by climb on slow cooling. These loops sometimes persist in quenched crystals.     

Thermoluminescence and optical absorption studies of NaCl: Gd2+ crystals

Thermal annealing of X-irradiated point defects in gadolinium doped NaCl crystal is investigated by Thermoluminescence (TL) and optical absorption methods. The results of the influence of pre-heat treatment and optical bleaching on glow curves and the production of Z₁-centres are discussed.     

Characteristics of traps in Tl2Ga2Se3S single crystals by low‐temperature thermoluminescence measurements

Defect characterization of Tl₂Ga₂Se₃S single crystals has been performed by thermoluminescence (TL) measurements at low temperatures between 10 and 70 K with various heating rate ranging from 0.6 to 1.0 K/s. The TL signal due to the luminescence from trap centers revealed one glow peak having maximum temperature of 36 K. Curve fitting and various heating rate methods were used for the analysis of the glow curve. The activation energy of 13 meV was found by the application of curve fitting method. This practical method also established that the trap center exhibits the characteristics of mixed (general) kinetic order. In addition, various heating rate analysis gave a compatible result (13 meV) with curve fitting as the temperature lag effect was taken into consideration. Distribution of traps was also investigated using an experimental method. A quasi‐continuous distribution was attributed to the determined trap centers.     

Electron microscopic investigations of precipitates in doped NaCl crystals

Precipitation morphology of NaCl:CdCl₂ and NaCl:SrCl₂ crystals is investigated by high voltage transmission electron microscopy. The volume fraction of the precipitates and the content of CdCl₂ has been evaluated using the theory developed by Hillard. Selected area diffraction patterns of the precipitates and investigations of the misfit dislocations around the precipitates is presented.     

Preparation and properties of ultratransparent NaCl single crystals

The preparation of up to 100 mm diameter single crystalline ingots of ultratransparent NaCl by injecting the reactive atmosphere is reported. The resulting material exhibits high optical quality and bulk absorption coefficient at 10.6 μm of 0.91 × 10⁻³ cm⁻¹, close to the intrinsic value, which makes it suitable for transmissive components in high-power CO₂ lasers.     

Special features of optical strength change in melt-grown NaCl crystals

The variation of the CO₂-laser pulse induced breakdown threshold has been studied experimentally in melt-grown NaCl crystals. An increase of the optical strength (up to two order of magnitude) is observed from the „top”︁ towards „bottom”︁ of the large diameter crystal boules, i.e. in the direction in which the impurities are driven away. The dependence of the threshold with the Ca²⁺ concentration demonstrates a complicated character of the effect of the impurity content on the optical strength of sodium chloride.     

Precipitation and dissolution of KCaCl3 impurity in NaCl crystals

Impurity precipitation in NaCl crystals containing CaCl₂ and KCl in various proportions is studied by means of flotation density measurements. The paper is concerned with the determination and dissolution, the kinetics and activation energy, and the mechanism of nucleation. Two temperature regions for solid solution decomposition were revealed. The characteristic stages in density variation upon isochronal annealing are shown to be correlated with radical changes in the X-ray diffraction patterns. Evidence is given that the nucleation is heterogeneous for the stable phase and homogeneous for the metastable one. – The activation energy in the low-temperature region has been found to be 0.8 ± 0.1 eV, which suggests precipitation to be diffusion-limited. From the kinetics studies it follows that the composition of the metastable phase corresponds to KCaCl₃ and the rate-controlling stage in stoichiometric crystals is a K⁺ diffusion.     

Influence of dopants and preparation method on the thermoluminescence properties of corundum crystals

Thermoluminescence (TL) of several types of corundum crystals is described. Undoped crystals showed a weak TL at 15 and 110°C with emission at 330 and 495 nm. Good TL response at 275°C is shown by Cr doped (0.03 wt%) crystals grown by Verneuil method in the oxygen cone of the flame annealed in hydrogen at 1500–1800°C. The most intensive TL response is shown by crystals doped with Ti and Mo (∼ 10⁻³wt.%) grown by Czochralski method in reducing conditions. The former may be used to the detection of γ-rays dose ≥ 10⁻³ − 10⁻² Gy, the latter ≥ 10⁻⁷ − 10⁻⁶ Gy.